The present invention relates to a virtual terminal control device for a switching system, and more specifically, to a virtual terminal control device for a switching system that hides a difference in call reference mode at a protocol control section from a basic call control section in a call processing section of the switching system. In the call processing section of the switching system, the protocol control section performs a process for each of protocols, where the number of simultaneously connectable call references differs depending on terminals to be employed. The basic call control section performs a basic call connecting process relative to the terminal and performs an added service control through a plurality of call references attendant upon the call connecting process. These control sections form a hierarchical structure and mutually send and receive signals, each of which is an event of a call reference dependence to achieve the call processing.
In the switching system, the call processing section performs the call connecting process. The added service process is of a hierarchical structure having a protocol control section performing a protocol process corresponding to a functional classification of employed terminals. Further, a basic call control section performs a basic call connecting process relative to a particular one of the terminals and further performs an added service control attendant upon the basic call connecting process. Based on the protocol, a primitive prescribed is used as an interface between the hierarchies. However, in the conventional call processing section, the function of the basic call control section and the function of the protocol control section are not clearly separated relative to a plurality of the protocol classifications. Thus, the process peculiar to the protocol also exists in the basic call control section.
In the foregoing conventional call processing section of the switching system, the basic call control section performs the process peculiar to the protocol. This raises a problem in that the basic control section must perform the process per protocol even when offering an additional service on the basic call control section. For solving this problem, a technique has been proposed where a virtual protocol control section is provided between the basic call control section and the protocol control section (see patent application Ser. No. 5-126676). The virtual protocol control section includes normalized data storing means for storing normalized data for normalizing a procedure from the protocol control section to a virtual protocol primitive as being a common primitive, normalized data managing means for recording or erasing the normalized data relative to the normalized data storing means, and normalized data selecting and executing means for normalizing the procedure from the protocol control section to the virtual protocol primitive based on the normalized data selected from the normalized data storing means. With this arrangement, the basic call control section controls the call connecting process and the added service process based on the normalized procedure from the virtual protocol control section so that the difference in procedure between the protocols can be hidden from the basic call control section.
On the other hand, the additional or added services offered by the switching system are classified as follows in view of handling the call:
(a) An added service, such as a recording service, which is realized on a single call (call reference). For example, an abbreviated dialing service in which a designated number is recorded as an abbreviated number, and making a call to the designated number is achieved by input of the abbreviated number. An absent-subscriber service in which a designated guide number is recorded due to absence of a user, and when a call is made to the user, a message is provided to a caller based on the recorded guide number.
(b) Another added service, which is realized when a multi-call (call references) is handled on the same terminal. For example, a transfer service in which a user of his busy terminal transfers his call to another number terminal. An in-communication incoming call notifying service in which an incoming call to a busy terminal is notified and switched.
Further, the terminals (and protocols) are also classified into unintelligent one capable of processing only one call and intelligent one capable of processing a multi-calls.
In the foregoing system having the virtual protocol control section between the basic call control section and the protocol control section, the number of call references relative to the same terminal in the protocol control is not normalized in the virtual protocol control section. Accordingly, in order to provide the added service in the plural call discrimination mode, the basic call control section is required to process separately depending on whether the number of processable call references at the terminal (protocol) is single or plural. Thus, it is difficult to realize all the added services without considering the protocol. Specifically, when the basic call control section is set to provide the added service in the plural call reference mode for the intelligent terminal (intelligent protocol control section), such an added service control process can not be directly applied to the unintelligent terminal (unintelligent protocol control section) in the single call reference mode, such as the analog terminal.